1. Field of the Invention
The present invention relates to an endless belt which can be used in a press apparatus such as an Extended Nip Press or Intensa S Press or the like for dewatering a wet web of paper in a paper making process.
2. Description of the Background Art
Recently, a so-called shoe press wherein, in the press part of a paper making process, dewatering of a web is carried out by pressing one surface of a web placed on a felt for enhancing the effect of dewatering the web with a rotary roll and pressurizing the other surface through an endless belt with a pressure shoe is becoming popular.
FIGS. 12 is a typical cross sectional view illustrating an Extended Nip Press as an example of such a press. Referring to FIG. 12, a pressure shoe 41 is arranged under a rotary roll 40. An endless belt 42 as a dewatering press is provided between rotary roll 80 and pressure shoe 41. Endless belt 42 is mounted and wound around guide rolls 43a and 43b and tension rolls 44a, 44b and 44c. A web 45 and felt 46 are passed between the endless belt 42 and the rotary roll 40.
If the rotary roll 40 is rotated in a direction indicated by arrow A, web 45 placed on felt 46 and endless belt 42 are moved in directions indicated by arrow B and arrow C, respectively. Web 45 and felt 46 are pressed strongly toward the rotary roll 40 by the pressure shoe 41 in the range of the pressure dewatering part P. Accordingly, web 45 is dewatered in pressure dewatering part P.
FIG. 13 is a typical cross sectional view illustrating an Intensa S Press as another example. Referring to FIG. 13, a cylindrical endless belt 52 for a dewatering press is provided under a rotary roll 50. A pressure shoe 51 pressing toward the rotary roll 50.through endless belt 52 is provided inside the endless belt 52. A web 54 and a felt 53 are passed between endless belt 52 and rotary roll 50. A pressure dewatering part P having a large width is formed between rotary roll 50 and pressure shoe 51. Web 54 is dewatered in pressure dewatering part P.
The following are endless belts for dewatering presses conventionally proposed for such shoe presses.
(1) a belt in which a synthetic resin such as polyurethane resin or rubber is impregnated into a base fabric of an endless belt from one of its surfaces (hereinafter referred to as a single coat type belt; U.K. Patent No. 2,106,555, U.K. Patent No. 2,106,557 and so forth)
(2) a belt in which an endless base fabric is embedded in a layer of synthetic resin or rubber (hereinafter referred to as a base fabric embedded belt: European Patent No. 194,602 and so forth)
(3) a belt in which a synthetic resin such as polyurethane resin or rubber is impregnated into an endless base fabric from both of its front and rear surfaces, and grooves are formed on the surface (hereinafter referred to as a double coat type grooved belt: U.S. Pat. Nos. 4,559,258, 4,908,103, 4,946,731 and so forth)
However, the above-described conventional endless belts for dewatering presses have problems as follows.
(a) Since all of the single coat type belt, the base fabric embedded belt, and the double coat type grooved belt use an endless base fabric impregnated with a synthetic resin or a rubber, the strength of the bond between the base fabric and the synthetic resin or rubber is small in such belts.
Particularly, in the case where layers disposed on both of the front and rear surfaces of the double coat type grooved belt are formed by the casting method, synthetic resin or rubber penetrates the base fabric from only one of the surfaces. Accordingly, it is not possible to cause the synthetic resin or rubber to penetrate the base fabric when the opposite surface is formed, so that a uniform anchoring effect from both sides cannot be obtained, and thus it is not possible to obtain a strong bond between the respective components. Therefore, there is the problem that, as the belt is used, a breaking away phenomenon is caused between the base fabric and the synthetic resin or the rubber which greatly reduces the life of the belt.
(b) An endless base fabric is normally formed of monofilaments such as polyamide fiber, polyester fiber, or the like. Such fiber is generally a material having hardness higher than the hardness of the synthetic resin or rubber. Therefore, when the endless base fabric is bent during the conveying of the belt, the endless base fabric tends to be subject to a concentration of stress, and a breaking away phenomenon tends to occur between the base fabric and the synthetic resin or the rubber. The life of the conventional belt is also made relatively short for this reason.
(c) Since the double coat type grooved belt is provided with grooves on its surface, moisture generated by dewatering of a web is held in the grooves. Therefore, the double coat type grooved belt has superior dewatering efficiency as compared with the single coat type belt. However, the double coat type grooved belt is formed on both its front and rear surfaces by the casting method or the like using a synthetic resin or a rubber. When one surface is formed after formation of the other surface, the texture of the base fabric is already tight, so that bubbles in the coating material do not disappear easily, and the belt is formed with the bubbles remaining. Accordingly, in the case of the double coat type grooved belt, such bubbles tend to be left in the resin or the rubber. If such a belt is used, white water which is pressurization during pressurizing of a rotary roll permeates from the bottom part of the grooves into the bubbles and further permeates from the bubbles into the base fabric. As a result, the breaking away phenomenon between the base fabric and a coating layer occurs at a relatively early time which shorten the life of the belt.
(d) In addition, the conventional endless belts use endless base fabric. The tensile force of filaments in endless base fabric is often not uniform, and it often happens that the base fabric is distorted in the belt during a manufacturing process thereof. Therefore, the entire belt tends to receive the distortion and is correspondingly deformed, or wrinkles or the like tend to be generated.
An object of the present invention is to solve such conventional problems and provide an enduring endless belt for a dewatering press in which no breakdown such as the breaking away phenomenon occurs and which can be used stably for a long time.
An endless belt according to the present invention is characterized in that a fibrous me is dispersed in a substantially uniform manner throughout a cylindrical endless elastic body layer.
According to the present invention, a cylindrical endless elastic body layer can be formed by impregnating a liquid elastic body precursor into a fibrous material and curing the liquid elastic body precursor.
Non-woven fabric may be used, for example, as the fibrous material to be impregnated with the liquid elastic body precursor. Non-woven fabric is natural fiber, chemical fiber, glass fiber, metallic fiber, or the like coupled by a chemical or physical method. Such non-woven fabric includes stitch bond non-woven fabric, needle punched non-woven fabric, spun bond non-woven fabric, melt blown non-woven fabric, spun lace non-woven fabric, wet laid process non-woven fabric, chemical bond type dry laid process non-woven fabric, thermal bond type dry laid process non-woven fabric, or air laid type dry laid process non-woven fabric and wet laid process non-woven fabric, or the like.
An organic fiber and/or an inorganic fiber is used as the material for a non-woven tape. Polyamide fiber, aromatic polyamide fiber, polyester fiber, polyacrylonitrile fiber, polyvinyl alcohol fiber, polyethylene fiber, polypropylene fiber, polyurethane fiber, polyvinyl chloride fiber, polystyrene fiber, polyfluoroethylene fiber, regenerated cellulose fiber, cotton fiber, or the like is used as the organic fiber.
Glass fiber, metallic fiber, rock fiber, or the like is used as the inorganic fiber. In addition, the non-woven tape may be formed of a mixed fiber, of an organic fiber and a inorganic fiber.
According to the present invention, polyurethane elastomer, acrylonitrile-butadiene copolymer, epichlorohydrin rubber, liquid rubber such as liquid polyurethane rubber, liquid nitrile rubber, liquid chloroprene rubber, liquid styrene rubber, liquid butadiene rubber, or the like, thermoplastic elastomer of polyurethane type, polyester type, polyolefin type, or the like, latex such as styrene-butadiene rubber latex, butyl rubber latex, polyurethane rubber latex or the like, or an emulsion such as polyurethane rubber emulsion, styrene rubber emulsion, nitrile rubber emulsion, or the like may be used as an elastic body or an elastic body precursor used in an elastic body layer.
The thermoplastic elastomer is made liquid by diluting it with a solvent for use and removing the solvent with heat or the like in the manufacturing process. According to the present invention, the liquid elastic body precursor includes such a thermoplastic elastomer diluted with solvent.
In cases where latex and emulsion are used, a dispersion medium is also removed with heat or the like during the manufacturing process of the belt.
In accordance with a preferred mode of carrying out the present invention, a non-woven tape impregnated with a liquid elastic body precursor is wound and layered in a cylindrical manner and integrated by curing the impregnated elastic body precursor.
In addition, according to the present invention, it is also possible to form a plurality of grooves on an outer peripheral surface of an elastic body layer in a circumferential direction. The grooves may be of a helical shape, a knurled shape, a diagonal lattice-like shape, or the like. It is possible to enhance the dewatering efficiency by forming such grooves as in the case of the conventional double coat type grooved belt.
According to the present invention, the mechanical strength can be reinforced by arranging reinforcing yarn-like bodies in an elastic body layer. The reinforcing yarn-like bodies are preferably arranged along a circumferential direction. In a case where grooves are formed on the outer peripheral surface or the like, the reinforcing yarn-like bodies are preferably arranged inside in the radial direction in the elastic body layer.
According to the present invention, an organic material and/or an inorganic material can be used as the reinforcing yarn-like bodies. Polyamide fiber, aromatic polyamide fiber, polyester fiber, or the like can be used as the organic material. Its shape may be of a bundle of filaments, yarn, roving, a cord, or the like. Glass fiber, metallic fiber, or the like may be used as the inorganic material. Its shape may be of roving, a cord, a wire, or the like.
According to the present invention, the mechanical strength in the circumferential direction and the width direction can be reinforced by arranging a reinforcing net-like material body in an elastic body layer.
According to the present invention, an organic material and/or an inorganic material can be used as the reinforcing net-like material body. Polyamide fiber, polyester fiber, polyvinyl alcohol fiber, or the like can be used as the organic material. Carbon fiber, metallic fiber, glass fiber, or the like can be used as the in organic material. Its shape may be of yarn, a cord, a wire, or the like. The meshes of the reinforcing net-like material body may be lattice-like shaped, lozenge-shaped, for example.
In addition, according to the present invention, the hardness of an elastic body layer in a part outside in the radial direction may be different from the hardness of the elastic body layer in a part inside in the radial direction. For example, it is possible to make the hardness in a part outside in the radial direction higher than the hardness in a part inside in the radial direction.
A manufacturing method according to the present invention includes the step of impregnating a liquid elastic body precursor into a tape-like fibrous material, winding and layering the tape-like fibrous material impregnated with the elastic body precursor on a supporter having an endless peripheral surface, the step of curing the elastic body precursor impregnated in the layered tape-like fibrous material to form an elastic body layer, and the step of removing the elastic body layer from the supporter.
In a case where an endless belt which is long in a circumferential direction such as an endless belt for Extended Nip Press or the like is manufactured, a supporter wherein a supporting belt is provided between a pair of rolls may be used.
In a case where an endless belt which is of a cylindrical shape as a whole and not so long in a circumferential direction such as Intensa S Press or the like is manufactured, a roll may be used as a supporter.
According to a manufacturing method in accordance with the present invention, a tape-like fibrous material impregnated with a liquid elastic body precursor is preferably wound on a supporter in a helical manner. It is possible to shift the tape-like fibrous material with a constant pitch while layering it to obtain an endless belt having a constant thickness with a desirable width.
In a case where an outer peripheral surface of an elastic body layer is cut and ground, it is preferable that the elastic body layer is worked before removed from a supporter. That is, it is preferable that the elastic body layer is cut and ground with the elastic body layer being wound on the supporter.
In addition, in a case where grooves are formed on the outer peripheral surface along a circumferential direction, it is also convenient to work an elastic body layer wound on a supporter.
In order to make it easy to remove an elastic body layer from a supporter, it is preferable that a mold release agent is applied on an endless peripheral surface of the supporter.
In a case where an endless belt in which reinforcing yarn-like bodies are arranged in an elastic body layer is manufactured, it is possible to arrange the reinforcing yarn-like bodies on a tape-like fibrous material to wind the reinforcing yarn-like bodies together with the tape-like fibrous material while winding the tape-like fibrous material on a supporter. In this case, it is possible to set the positions of the reinforcing yarn-like bodies in the elastic body layer of the belt in accordance with the positions of the reinforcing yarn-like bodies on the tape-like fibrous material. For example, it is possible to adjust the positions of the reinforcing yarn-like bodies so that the reinforcing yarn-like bodies are arranged more close to the side of the supporter of the elastic body layer, i.e., inside in the radial direction.
In addition, it is also possible to adjust the degree of reinforcement achieved by reinforcing yarn-like bodies by adjusting the number of the yarn-like bodies during winding of the reinforcing yarn-like bodies together with a tape-like fibrous material.
In a case where an endless belt in which reinforcing net-like material body is arranged in an elastic body layer is manufactured, it is possible to arrange the reinforcing net-like material body on a tape-like fibrous material to wind the reinforcing net-like material body together with the tape-like fibrous material while winding the tape-like fibrous material on a supporter. It is also possible to wind the above tape-like fibrous material on a supporter, then wind reinforcing net-like material body on the fibrous material, and further wind a tape-like fibrous material thereon.
According to a manufacturing method in accordance with the present invention, a tape-like fibrous material impregnated with a liquid elastic body precursor is wound on a supporter with a predetermined tensile force. The tensile force of winding may be selected suitably. For example, in a case where a non-woven tape having a width of 165 mm is used as the tape-like fibrous material, the tensile force of the winding is generally in the range of 5 kg to 10 kg. The thickness of a belt manufactured by this manufacturing method can be adjusted in various ways. For example, in a case where it is wound on a supporter in a helical manner, it is possible to adjust the thickness of a belt by changing the pitch with which the tape-like fibrous material is shifted. In such a case, generally, it is possible to increase the thickness of the belt by making the pitch smaller, and to reduce the thickness of the belt by making the pitch larger.
In addition, after a tape-like fibrous material is once wound on a supporter, it is possible to further wind a tape-like fibrous material thereon. In this case, it is possible to use a different type of tape-like fibrous material or elastic body precursor to be impregnated. It is also possible to manufacture a belt in which the hardness in the inside part of the belt and the hardness in the outside part of the belt are different by using different types of elastic body precursor or the like, for example, using elastic bodies having different molecular weights in the inside and outside parts of the belt.
According to the present invention, curing of an elastic body precursor can be performed by heating or leaving at room temperature, for example.
It is apparent that working of an endless belt may be performed after it is removed from a supporter. For example, it is possible to cut and grind an outer peripheral surface of the belt after it is removed from the supporter. An inner peripheral surface of the belt may be also cut and ground if necessary.
In an endless belt for a dewatering press in accordance with the present invention, a fibrous material is dispersed in a substantially uniform manner all over an elastic body layer. Therefore, the whole belt is unified, and, unlike the conventional belt, different materials or materials having different strength are not bonded, so that the belt itself is not broken away.
In addition, the whole is uniform, so that stress is also applied uniformly to the whole of it, and it does not happen that large distortion is received inside the belt.
Endless base fabric in which the tensile force of filaments tend to be not uniform is not used, so that the belt is not distorted as in the conventional case.
According a manufacturing process of the present invention, a tape-like fibrous material impregnated with a liquid elastic body precursor is wound and layered on a supporter, and the elastic body precursor is cured to form an elastic body layer. The tape-like fibrous material impregnated with the liquid elastic body precursor is layered and bonded by the liquid elastic body precursor to be integrated. Therefore, the tape-like fibrous material cured after layered is in the state wherein the fibrous material is uniformly dispersed and contained in the elastic body layer.
According to this manufacturing method, it is possible to obtain an endless belt of desired shape and structure freely by changing the shape and size of a supporter or by changing the width of the tape-like fibrous material or the number of layers to be layered. Accordingly, it is possible to manufacture an endless belt adapted to wider application as compared with the conventional endless belt using endless base fabric.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.